Simulations were used to examine the research subject in detail and to find alternative solutions for renovation. Wind and temperature differences and the building on the whole were taken into account. Simulations were made with IDA ICE –software: one staircase including its apartments was modeled. The software proved to be suitable for modeling natural ventilation in Finland’s climate. In the quantitative part of the study, indicators were made to describe the effects of different solutions to ventilation and indoor air. Three alternative solution models were made that differ the most in the compactness of the external parts and the disposition of air inlet valves in the building.

This research study produced information about the significance of compactness on the functionality of ventilation as well as about air flows in different weather conditions. On the basis of the results found in this study, indicators were developed to describe the suitability of the solutions for good air ventilation in indoor air. The reliability of quantitative results was ensured by comparing them to the results received from previous studies and also with model testing.

Both qualitative and quantitative research gave a good overall picture of problems in the research subject but also on a general level. New information was received on the pressure differences of the building: the leaks in the external envelope of the bulding have an influence on wind driven pressure differences on external walls ¬– larger leaks even out airflow through air inlet valves. Also, more compact building together with fresh air valves lowers the effect of apartment’s outdoor leaks to its ventilation. It is a common impression that compacting external walls weakens the proper functioning of natural ventilation, for example, by turning the air flow from ventilation chimney towards the apartment, and the findings of this study corroborate this common impression. This study indicates that it is not enough to measure CO2-levels in indoor air alone when the goal is to obtain good ventilation for the benefit of both energy efficiency of the building and human wellbeing.